1. Field of the Invention
The present invention relates to radios for use in vehicles, and, more particularly, to maintaining a dynamic list of FM stations in radios for use in vehicles.
2. Description of the Related Art
Driver and user personalization is a recent trend that has a potential to impact the automotive and consumer entertainment market. Original Equipment Manufacturers have taken notice of this trend and are making the radio head unit human machine interaction more intuitive, thereby differentiating their offerings to the end consumer.
One area that offers room for improvement is the navigation of FM stations. In state of the art user navigation procedures to preview valid station frequencies that can be clearly received by the radio, the user tunes, seeks or scans to a station.
OEMs have begun to require radios to provide FM station lists in order to ease the navigation user experience. An FM station list may be a list of FM stations in the vicinity of the user which are of a certain signal reception quality. Each of the stations in the FM station list may be associated with a respective pushbutton on the human machine interface, and thus the user need only push the respective pushbutton in order to tune in the station. The FM station list may enable the user to conveniently select viable stations of good signal quality without having to manually tune, seek or scan to the stations in a sequential manner (e.g., in either increasing or decreasing frequency order).
A method that OEMs have defined to allow updating of the FM station list is through the offering of a manual station list update option. When this scheme is triggered, it mutes the currently tuned-to station audio and starts to scan the FM frequency band. Stations that meet particular fieldstrength, multipath, and adjacent channel interference criteria are populated onto the FM station list. During the time period in which the FM station list is being populated, the user is presented with a visible progress bar which displays the status of the update.
A reason why the above-described FM station list population procedure is not efficient in a single tuner environment is that once a station list update has been completed, its validity is a function of the geographic location of the vehicle. Thus, if the mobile user drives away from the geographic location at which the last manual station list update was performed, then the FM station list becomes “stale.” Accordingly, the user is required to again do a manual station list update to avoid the possibility of going into the FM station list and choosing a now-invalid station, which would result in poor audio reception.
As an example case in point, assume a user does a manual station list update in Georgia and drives to Indiana without doing a manual station list update. If he then enters the FM station list, the list would not clearly reflect the true nature of actual stations available in the area. With this being the case, it is possible that if a user does select a station frequency from the FM station list menu, the selected frequency is likely to not correspond to a station that has good reception at the user's current location in Indiana. Rather, the user is likely to receive a noisy signal that is of unacceptable listening quality.
One way to overcome the above-described problem of the FM station list not being updated is through the costly use of a dual tuner radio. Specifically, a dual tuner radio can update the FM station list in a manner that is imperceptible to the end user by virtue of the second tuner performing background scanning without affecting the audio path of the main tuner which is being listened to by the user.
In order to prevent wrong audio modulation to be heard during AF switch, the prior art employs dual tuner radio variants. In cases where prior to an AF switch, the PT code is not received, dual tuner radios employ what is termed as an audio correlation algorithm. The algorithm may be implemented by tuning the main tuner and second tuner to the source and target frequency, gathering the audio data, and employing auto-correlation methods to define their correlation. This may take between two and five seconds worth of audio sampling. The audio correlation algorithm requires royalty payments for dual tuner variants.
Accordingly, what is neither anticipated nor obvious in view of the prior art is a method of performing automatic updates of an FM station list in a single tuner environment without the user perceiving the occurrence of the updates, and without the user's listening experience being interrupted by the updates.